Rotary compressor with oil cooling

ABSTRACT

In a rotary-type compressor for a refrigeration plant, a lubricating oil cooling system which utilizes a portion of the condensed refrigerant as coolant for the oil and feeds back the refrigerant to the compressor at a point where the pressure levels of the compressor and the returning refrigerant are substantially equal.

United States Patent [191 Brandin et al.

[4 June 28, 1974 ROTARY COMPRESSOR WITH OIL COOLING [75] Inventors: ToreBrandin; Anders Lundberg,

both of Norrkoping, Sweden [73] Assignee: Stal Refrigeration,Norrkoping,

' Switzerland 221 Filed: Dec. 14, 1972 21 Appl. No.: 314,989

[52] US. Cl. 62/193, 62/470 [51] Int. Cl. F25!) 31/00 [58] Field ofSearch 68/84, 192, 193, 196, 468,

[56] References Cited UNITED STATES PATENTS 2,155,051 4/1939 Kagi 62/4702,875,592 3/1959 Olsen 62/470 3,379,033 4/1968 Grant.... 62/84 3,710,5901/1973 Kocher 62/470 Primary Examiner-Meyer Perlin ABSTRACT In arotary-type compressor for a refrigeration plant, a lubricating oilcooling system which utilizes a portion of the condensed refrigerant ascoolant for the oil and feeds back the refrigerant to the compressor ata point where the pressure levels of the compressor and the returningrefrigerant are substantially equal.

12 Claims, 7 Drawing Figures PATENTEDJBMZa I914 sum 1 [IF 2 1 ROTARYCOMPRESSOR WITH OIL COOLING BACKGROUND OF THE INVENTION Cooling thelubricating oil for a refrigeration compressor by means of water, air,or brine has been known, but each of these media creates difficultproblems. Water-cooling, for example, demands an adequate supply ofreasonably good quality water; air coolers tend to be large andexpensive; and cooling by brine makes heavy demands on the material inthe cooler.

SUMMARY OF. THE INVENTION This invention is based on the use of thecompressed and condensed refrigerant fluid of the refrigeration plantfor cooling the lubricating oil. Cooling is effected by means of aheat-exchanger, which may be designed either with separate paths for thetwo fluids or in the form of a mixing chamber cooler, in which the twofluids are mixed directly, and which may be supplemented by a device forsubsequent fluid separation. The refrigerant, completely or partiallyevaporated in the oil cooling process and possibly mixed with more orless of the cooled'oil is fed back to thecompressor.

It would seem most obvious to return the used refrigerant to the suctionside of the compressor. This, however, would cause a capacity loss inthe refrigeration plant corresponding to the amount spent refrigerant tobe fed back.- I

' Another possibility is to provide a pump for compressing and feedingback the used refrigerant to the high-pressureside of the plant. Theintroduction of an extra pump component, however, even if small inrelation to the compressor, requires extra service and increases therisk of breakdowns occurring in the refrigeration plant.

This invention proposes, therefore, to utilize the inherent design ofthe rotary compressor, which may be, for example, a screw compressor,sliding van compressor, or the like. Such a compressor has a continuousand uniform pressure rise through its working compartment, and thisfeature is utilized in the invention by feeding the refrigerant used inoil cooling back to the compression chamber at a point where thepressure levels of the compression chamber and of the returningrefrigerant are substantially equal. In this way, the power requirementof the compressor increases slightly, but the capacity remainsunchanged. It should be noted that this invention concerns compressorsof relatively large capacity, and that the power for cooling the oil issmall in comparison with the total capacity of the compressor. A smallincrease in the power requirement of the compressor will, therefore, dono harm, provided that the rated power of the compressor motor hassufficient margin. A reduction of the resultant power of the compressor,on the other hand, could be undesirable.

While the principle of feeding back refrigerant to a pressure levelbetween the inlet and outlet sides of a compressor is known. and hasbeen disclosed in US. Pat. No. 3,568,466, it has not been applied tocooling the lubricating oil.

The primary object of the invention, therefore, is to provide alubricating oil cooling system for refrigeration compressors of therotary type using the refrigerant as a cooling medium and returning thespent refrigerant to a pressure level in the compressor substantiallyequal to the pressure of the refrigerant being fed back.

DRAWINGS FIG. 1 shows diagrammatically an oil cooling system for arefrigeration compressor of the rotary type in which the oil cooler is aheat exchanger;

FIG. 2 shows diagrammatically an oil cooling system in which the oilcooler is a mixing chamber;

FIG. 3 is a diagrammatic showing of the mixing chamber of FIG. 2 ingreater detail and with possible variations;

FIG. 4 diagrammatically discloses a combined oil separator and oilcooler;

FIGS. 5 and 6 show diagrammatically two modifications of a combined oilseparator/oil cooler; and

FIG. 7 shows diagrammatically a modified form of the mixing chamber ofFIG. 3.

DESCRIPTION OF THE EMBODIMENTS According to FIG. 1, refrigerant issucked through tube 1 from the low-pressure side of the refrigerationunit to the compressor 2, where it is compressed and conducted to an oilseparator 3 through tube 16. Oil

separator 3 may be combined with oil container 4 of the oil system. Fromoilseparator 3 the refrigerant is led further to the condenser 5 of therefrigeration unit, where it is cooled, condensed and conducted furtherto a receiver (not shown), if any, or to the low-pressure side throughtube 6. One side of the oil cooler 7 is coupled to the liquid side ofthe refrigeration unit through tube 8 from the liquid tube 6. One sideof the oil cooler 7 is coupled to the liquid side of the refrigerationunit through tube 8 from the liquid tube 6 shown in FIG. 1, or directlyto condenser 5 or to the receiver. The amount of refrigerant supplied iscontrolled by a control valve 9 in tube 8.

I'Iot oil from oil container 4 is led to oil cooler 7 through tube 18.By absorbing heat from the hot oil in oil cooler 7 (here shown as a heatexchanger), the refrigerant is vaporized and is then supplied to theworking compartment of compressor 2 through tube 11 to a port 10 locatedin compressor 2 in such a way that the pressure at this point is higherthan the low pressure of the refrigeration unit and lower than its highpressure. By reintroducing the refrigerant at this location incompressor 2, no capacity loss is encountered, at the expense of a verysmall power increase of compressor 2. Depending on how port 10 ispositioned, this increased power requirement can be minimized. Thecooled oil may be supplied to compressor 2 by its own pressure.

A control device 12 may be introduced in tube 11 between oil cooler 7and compressor 2, with the help of which the oil temperature can becontrolled by adjusting the outlet pressure of the refrigerant. Also, apump 13 may be provided to pump the oil to compressor 2 through oilcooler 7..

FIG. 1 also shows that oil tube 14, connecting oil cooler 7 andcompressor 2, may be branched so that oil for injection into the workingcompartment of compressor 2 is conducted into port 10 of compressor 2together with the refrigerant through regulating valve 15.

Regulating valve 9 in refrigerant inlet tube 8 to oil cooler 7 iscontrolled by therrnosensitive members 17 or 17'. Thermosensitive member17 is inserted in refrigerant outlet tube 11 from oil cooler 7. In thisway, the cooled oil in tube 14 will be maintained at a fairly constanttemperature. Alternately, a thermosensitive member 17 may be placed inoutlet tube 16 from compressor 2, the regulating valve 9 thus beingcontrolled by the outlet temperature of compressor 2.

FIG. 1 also shows that an oil pump 13 may be inserted in oil outlet tube18 from oil container 4, in this way ensuring sufficient oil pressure intube 14, as well as in the bearing of compressor 2 and other points of15 lubrication.

It is evident that components 1-6 and 16 constitute the conventionalelements of a rotary type refrigeration compressor, whereas parts 7-11,plus 14, 18, and 17 or 17 comprise the framework of the oil coolingsystem of this invention, and, as mentioned, control device 9 may beregulated by one of the therrnosensitive members 17 or 17. Elements 12,13 and15,.on the other hand, are selectively supplementary parts whichmay be employed according to the needs of a 'given situation.

FIG. 2 describes another version of an oil cooling system in accordancewith this invention, wherein oil cooler 7'is shown as a mixing chamberfor direct cooling of theoil by'admixing it with refrigerant fromcondenser 2. Reference characters for the same parts are identical withthose of FIG. 1, and it is clear that the arrangement of components inthis embodiment is the same as that of FIG. 1.

FIG. 3 shows mixing chamber 7 of FIG. 2 in some detail, aswell as somevariants in the system. Refrigerant tube 8 with its regulating valve 9and oil tube 18 are both connected to oil cooler mixing chamber 7 atinner chamber 20 within a cylindrical baffle '19, outside of which thereis anoil chamber 21. Above chambers 20 and 21 a scumremoving layer 22may be placed, which in its simplest form consists of a net or coarsefilter of metal wire or the like.

The refrigerant which enters the central chamber 20 together withtheihot oil will vaporize, and the gaseous refrigerant which may beintermingled with some oil foam, is led by tube 11 through regulatingvalve 12 to intake 10 on compressor 2. The oil fro oil chamber 21 goesthrough tube 14 to compressor 2. Tube -14 may be divided into two partsas shown, one of which leads to 8 and outlet tube 11. Tube bundles 23,24 are surrounded by a casing 26, inside which a baffle 25. is fixed, tothe center of which outlet tube 14 for the oil is connected. In thisway, the oil, which drips down from oil separator 3 into oil container4, will follow the path marked by arrows through cooling casing 26; thatis, through the bottom of casing 26 parallel to tube 14, and thereafterupward and outward, around the edges of baffle 25'and inward throughtube bundle 24 to the center of baffle 25, where the oil leaves cooler 7through outlet tube 14.

FIG. 6 shows an oil cooler 7 according to the mixing principle of FIG.2. At the bottom of oil separator 3, oil container 4 is defined by abaffle 27. Condensed refrigerant'is conducted to the bottom of oilcontainer 4 through tube 8 and regulating valve 9, which is herecontrolled by a temperature sensitive element 17 on oil outlet tube 14.Oil from compressor 2 is separated in oil separator 3 and runs downthrough it, optionally through a scum-removing filter 22' correspondingto scum remover 22 of FIG. 3. The vaporized refrigerant from oilcontainer 4 moves upward and can either be brought back to intake 10 oncompressor 2 through tube 11, or can be mixed with the hot refrigerantin separator 3 and from there proceed to condenser 5. FIG. 7 shows afurther variant of mixing chamber 7' of FIG. 2. An extra mixing chamber28 has been added to the side of mixing chamber 7'. Refrigerant tube 8and oil tube 18 are connected to side wiring chamber 28, from which themixture of oil and refrigerant enter the main mixing chamber 7, in whicha scum-remover 22" in theform of a coarse metal wire filter has been Imounted. Oil outlet tubel4 is connected to the bottom of mixing chamber7, .while refrigerant outlet 11 is connected to the top.

According to FIGS. 2, 3, 6 and 7, through tubes 11 and 14, oil andrefrigerant, respectively, and various mixtures of these two fluids, maybe supplied to coman extra intake 10' on corn ressor 2, whereas theother part of tube 14 leads to bearings and other points of lubricationon compressor 2, possibly through oil pump 13'. It is also possible toconduct part of the oil from tube 14 to refrigerant tube 11 as shown bythe dashed branch tube carrying regulating valve 15, and thus thisportion of oil would be brought to intake 10 along with the refrigerant.

FIG. 4 shows a variant of FIGS. 1 and 2 where oil cooler 7 or 7 is builtinto oil container 4 in oil separa: tor 3. The more detailedconstructions of combined oil separator/oir cooler are shown in FIGS- 5and 6, FIG, 5 corresponding to the heat exchanger of FIG. I, and FIG. 6corresponding to the mixing chamber '7' of FIG. 2.

In FIG. 5 the oil cooler 7 comprises tube bundles 23, 24 introducedbetween vertical extensions of inlet tube pressor 2 at suitablelocations.

It is clear that the different elements for controlling and regulatingthe various flows may be used or omitted according to the specific needsof any individual situation. In this way, the invention foresees manydifferent possibilities for combination in the refrigeration systemwithout departing from its scope. In addition, it should be noted thatthe principles of this invention may be applied to multi-stagecompressors of different kinds, the refrigerant from oil cooler 7 or 7being fed back to the compressor between any pair of these stages. I

What is claimed:

1. In a refrigeration compressor (2) of the rotary type, in which oilfor lubrication of the compressor and refrigerant together leave theoutlet side of the compressor and are brought to an oil separator (3)from which the refrigerant flows to a condenser (5), an oil coolingsystem which comprises:

an oil cooler (7), to which the oil flows from the oil separator; and

the. compressor being provided with an intermediate intake port (10)between its inlet and outlet sides (1, 16 respectively), wherein aportion of the condensed refrigerant is sup plied to'said oil cooler forcooling the oil, from whence this portion of refrigerant is fed back tothe compressor through said intake which is positioned at a pressurelevel of the compressor which substantially corresponds to the pressureof the refrigerant leaving said oil cooler.

2. Oil cooling system according to claim 1, wherein the refrigerant issupplied to said oil cooler (7) through a regulating valve (9).

3. Oil cooling system as defined in claim 2, wherein said regulatingvalve (9) is controlled by the temperature on the outlet side (11, 14)of said oil cooler (7, 7' respectively).

4. Oil cooling system according to claim 2, in which said regulatingvalve (9) is controlled by the temperature on the outlet side (16) ofthe compressor.

5. Oil cooling system as described in claim 1, further comprising aconstant pressure valve (12) for the refrigerant operatively connectedbetween said oil cooler (7) and said intake on the compressor.

6. Oil cooling system according to claim 1, wherein said oil cooler (7forms the bottom portion (4) of the oil separator (3).

7. Oil cooling system according to claim 1, wherein said oil cooler (7is a heat exchanger through which the oil and the refrigerant flowseparately.

8. Oil cooling system as defined by claim 7, wherein the oil and therefrigerant are returned to the compressor (2) separately.

9. Oil cooling system according to claim 7, wherein part of the cooledoil from said oil cooler (7 may be diverted through a branch line valve(15) and returned to the compressor (2) together with the refrigerantthrough said compressor intake (10).

10. Oil cooling system according to claim 1, wherein said oil cooler(7') is a mixing chamber where oil and refrigerant are mixed for coolingthe oil before both fluids are returned to the compressor (2).

11. Oil cooling system according to claim 10, wherein said oil coolermixing chamber (7') comprises a part of the oil separator (3) on itsinlet side, separate outlet means (ll, 14 respectively) for oil andrefrigerant being provided on the oil separator.

12. Oil cooling system according to claim 11, wherein pan of the cooledoil is supplied to a second intake port (10) situated between the inletand outlet sides (1, 16 respectively) of the compressor (2).

mm PC1-1050 (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent 103 820350 1 ated n 1 3 1974 lnventor(s) Tore Brandin;Anders Lundberg It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

[30] Foreign Application Priority Data December 22, 1971 Sweden.16463/1971 Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents QSCOMM-DC 60376-P69 1: us GOVERNMENT PRINTING orncs lass03s6-:w\v

1. In a refrigeration compressor (2) of the rotary type, in which oilfor lubrication of the compressor and refrigerant together leave theoutlet side of the compressor and are brought to an oil separator (3)from which the refrigerant flows to a condenser (5), an oil coolingsystem which comprises: an oil cooler (7), to which the oil flows fromthe oil separator; and the compressor being provided with anintermediate intake port (10) between its inlet and outlet sides (1, 16respectively), wherein a portion of the condensed refrigerant issupplied to said oil cooler for cooling the oil, from whence thisportion of refrigerant is fed back to the compressor through said intakewhich is positioned at a pressure level of the compressor whichsubstantially corresponds to the pressure of the refrigerant leavingsaid oil cooler.
 2. Oil cooling system according to claim 1, wherein therefrigerant is supplied to said oil cooler (7) through a regulatingvalve (9).
 3. Oil cooling system as defined in claim 2, wherein saidregulating valve (9) is controlled by the temperature on the outlet side(11, 14) of said oil cooler (7, 7'' respectively).
 4. Oil cooling systemaccording to claim 2, in which said regulating valve (9) is controlledby the temperature on the outlet side (16) of the compressor.
 5. Oilcooling system as described in claim 1, further comprising a constantpressure valve (12) for the refrigerant operatively connected betweensaid oil cooler (7) and said intake (10) on the compressor.
 6. Oilcooling system according to claim 1, wherein said oil cooler (7) formsthe bottom portion (4) of the oil separator (3).
 7. Oil cooling systemaccording to claim 1, wherein said oil cooler (7) is a heat exchangerthrough which the oil and the refrigerant flow separately.
 8. Oilcooling system as defined by claim 7, wherein the oil and therefrigerant are returned to the compressor (2) separately.
 9. Oilcooling system according to claim 7, wherein part of the cooled oil fromsaid oil cooler (7) may be diverted through a branch line valve (15) andreturned to the compressor (2) together with the refrigerant throughsaid compressor intake (10).
 10. Oil cooling system according to claim1, wherein said oil cooler (7'') is a mixing chamber where oil andrefrigerant are mixed for cooling the oil before both fluids arereturned to the compressor (2).
 11. Oil cooling system according toclaim 10, wherein said oil cooler mixing chamber (7'') comprises a partof the oil separator (3) on its inlet side, separate outlet means (11,14 respectively) for oil and refrigerant being provided on the oilseparator.
 12. Oil cooling system according to claim 11, wherein part ofthe cooled oil is supplied to a second intake port (10'') situatedbetween the inlet and outlet sides (1, 16 respectively) of thecompressor (2).